Radio communication system



Dec. 25, 1934. KOCH RADIO COMMUNICATION SYSTEM Filed Dec. 51, 1929 4 Sheets-Sheet 2 H wk r llllll lllllllllllllllllllllllllllllllllllll llnllllllllllL Ear] {f0 Z2.

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4 Sheets$heet 3 E. L. KOCH RADIO COMMUNICATION SYSTEM Filed Dec. 31, 1929 Dec. 25, 1934.

Dec. 25, 1934; E. KOCH RADIO COMMUNICATION SYSTEM Filed Dec.

51, 1929 4 Sheets-Sheet f v H ma w n a. b m

a 7 \mw m 5 on much'narrower frequencybandsthan those' Patented Dec. 25, 1934 UNITED STATES, TE T-spun]: 1...)...g ii illlgtsysm I I I v I Earl lii KochxChicago; mesne assignments, toEarl L. KochHolding Corporation; New Iiork,.N. jY., :acorporation of New Application Decemben 31, 1929, S erialNo. 417, 34

" 6 Claims. 2,,(01. 250 -17) This invention relates to high frequency radio communication systems, and it has among its ob jects the provision of improved radioitrans'mittiiig and radio receiving systems capable ofoperating used heretofore, and thereby enabling the "establishment of a much larger number of practically useful communication channels within the available radio spectrum. q

The novel features and. principles of the inv'ention will best be understood from the followin description of a radio communication system exemplifying the invention, reference being had to the accompanying drawings wherein Fig. 1 to the left, illustrate diagrammatically a five channel radio transmittin'g system embodying the invention; and 1 t j Figs. 3 and 4, when placed end to end, with, Fig. 3. to the left, illustrate a five channel radio receiving system embodying the invention.

In point to point radio telegraph communication systems, messages are tran'smitted overdefinitely assigned frequency channels which are allocated to the stations of the systems. Each channel is of a definite mean frequency andthe stations operating within the channel are not permitted to deviate from this mean frequency beyond a predetermined degree. y l

- At the present time, there is available for point to point communication systems in the high frequency range the frequency bandextending from 1500 kilocycles to 23,000 kilocycles; Of this frequency range, the band, extending from 1500 kilocycles to 6000 bilocycles is known as the continental high frequency band and has been assigned for use in point to point communication over the continent.

In the present state of the art, it is generally considered that the separation between themean frequencies of the individual communication channels in these bands must be 0.2% of the free quency assigned to a particular channel." Thus, a channel having an assigned frequency of 6,000

kilocycles must includes a frequency band of 12 Figs. 1 and 2, when placed end to end; with mercial use, nor to the particular frequency band, but itsfeatures are applicable and useful to improveradio' communication systems, to decrease the channel separation necessary for efficient op eratio'nof such systems, and to generally provide more efficient, simple and reliable radio communication' "between widely spaced points. Through, the use of ithe invention, it is possible to providemany more communication channels withinthe available radio spectrum than with the systems known heretofore, each'channel being capable of operating without interfering with the adjacent channels and without being disturbed by signals transmitted in these channels.

For'purposes of illustration, it is assumed that there was made available for communication purposes one of the official short wave channels,

say a channel having a frequency of 5,875 .kilocycles; On the basisof the permissible deviation of '.2 ofthe assigned frequency, this channel will have assignedfor itsuse'a frequency band extendingrfrom 5,869.125ki1oc'ycles to 5,880.875 kilocycles. By utilizing the apparatus and arrangements of. the invention, I have obtained practical point to point commercial telegraphic communication within the band of frequencies as-. signed to such channel through five distinctcommunication subchannels, each subchannel operating in the'same way as a normally assigned channel isintended to operate. In practice, it has been found convenient to have these subchannels separated by a frequency band of 750 cycles, although a larger number of subchannels may be provided within the assigned frequency band by following the principles of the invention;

In the drawings, there is illustrated such five subchannel communication systems intended to operate with a frequency separation of 750 cycles between the individual subchannels. fAssuming, for the'purpose of'illustration, an assinged frequency of 5,875 kilocycles; the individual subchannels are arranged to operate so that the first subchannel operates with a frequency of 5,873.50 kilocycles, the second subchannel with afrequency of 5,874.25 kilocycles, the third subchannel with a frequency of 5,875.00 kilocycles (this being the assigned channel frequency) the fourth subchannel with a frequency of 5,875.75ki1ocycles, and the fifth subchannel with afrequency of 5,876.50 kilocycle's. In the drawings, the five subchannels of the transmitting system shown in Figs. 1 and Z'and the five subchannels of the receiving system shown' in Figs. 3 and 4 are identified by numerals C1 to C5.

The individual subchannels are, in general, provided with the same kind of apparatus, and they are arranged in the same way, so that it will only be necessary to describe in detail the apparatus and arrangement of a single subchannel and point out only its relationship to the apparatus and the arrangements of the other subchannels in order to fully understand the invention. l V

The transmitting system comprises the transmitting apparatus which is shown in Fig. 2 and the monitoring apparatus which is shown in Fig.

l. The transmitter apparatus comprises a transmitting oscillator T0 in which ismaintained a continuous high frequency oscillation of the frequency on which the particular subchannel is to operate, a transmitter amplifier TA in which the high frequency oscillations maintained in the transmitting oscillator are amplified andsubjected to control action, such as keying, for'trans mission of signals; and a transmitter power amplifier TPA in which the oscillatory output of the transmitter amplifier TA is further amplifiedto a value suflicient to'secure radiation that would reach the point with which the particular channel is to maintain communication. The power amplifier is associated with suitable. radiating apparatus, such as an antenna RA.

The transmitting oscillator TO comprises a pair of audion tubes V1, V2 of the four-element or screen-grid type including, respectively, filamentary cathodes 2, 3, control grids 4 and 5, anodes or plates 6 and 7, and screen grids 8 and 9. The cathodes 2 and 3 are supplied with heating current from a suitable source, such as a cathode heating battery 10, one leg of the cathode filae mentsbeing connected to a grounded bus bar which is indicated on the drawings by the letter G. In the output circuits of the two tubesVl, V2 are connected resonant tank circuits L01, L02 formed of inductances 11 and condensers 12. Plate current is supplied to the output circuits of the two tubes V1, V2 from .a suitable sourceof uni-directional current such as a battery 14 which is connected to the two plate circuits .through high frequency chokes 15, 16. A bridging condenser 18 and 19, respectively, between each tank circuit and cathode provides a by-pass for the high frequency currents and completes the output circuit of each tube.

The input circuits of the two tubes V1 and V2 comprises impedances 20, 21, respectively, and

by-pass condensers 22, 23. Biasing means such.

as batteries 2% serve to maintain the grids of the tubes at a suitableoperating potential with re spect to the cathodes. The screen grids 8 and 9 of the two tubes V1, V2 are connected to the cathodes through by-pass condensers 26 .and are maintained at a positive potential against the cathodes through a connection to a suitabletap 28 on the plate battery 14 to'prevent feed-back from the output circuit'to the input circuit of each tube through the inter-electrode capacity.

The two'tubes V1, V2 with their associated circuits are coupled into'a ring circuit by means of coupling condensers 29, 29 connected between the control grid of the one tube and output cir cuit of the other tube, respectively.

The two tank circuits LCl and LC2 are tuned to the frequency of the oscillation that is to be used in the particular subchannel. Each tank circuit will accordingly form a filter unit or section which will maintain and build up oscillations of the frequency to which it is tuned but will suppress and absorb other frequencies. The Q011 pling between the input circuit of each tube and the output circuit of the preceding tube in the ring circuit may be made through the medium of adjustable taps 30, 31 on the inductances 11 of the tank circuits L01, L02. This coupling is made weak so that only a small amount of the energy of the output circuit of one tube is impressed upon the input circuit of 'the' next successive tube of the ring circuit. r

A circuit arrangement as described above when This action results from the fact that theaoscillatory currents are continuously recirculate'd through filter circuits which are resonant -to the-desired frequency but absorb or are opaque to all other frequencies. There is thus formed, in

eifect a filter with an infinite number of filter sections, The electron tubes serve to secure oneway circulation of the current through the filter sections so as to compel the currents to pass over again and again through the filter sections where the currents of the frequency to which the circuit is tuned is built up and all other currents are suppressed. For the eifectiveness of this arrangement it is important that the electron tubes which are used as coupling means shall not feed back energy directly from the output electrodes into the input electrodes without passing it first through the filter circuits.

' This stabilizing high frequency oscillator thus forms a reentrant ring oscillator having filter elements and amplifier tubes interconnected in a ring circuit to continuously re-feed the current only in one direction, the individual amplifier tubes being connected to derive only a small amount of energy from the preceding filter section and to supply it in amplified form to the next filter section, under substantial elimination of direct feed back between the output and input electrodes of the individual tubes.

In accordance with my invention I employ such reentrant ring oscillator as a primary oscillator for each communication subchannel to stabilize the oscillations within the subchannel. I have found that such reentrant ring oscillator retains a particularly high degree of stability if used with low energies and when so used it will maintain the frequency of the oscillations for which the filter circuits are designed with an extremely high degree of accuracy. According to the invention such reentrant ring oscillator operating with low energy is utilized to obtain high power oscillations suitable for radio transmissions in signalling systems by applying oscillatory energy from such ring oscillator to the input electrodes of a power amplifier the output of which is to be used for radiation. In the preferred arrangement, the oscillatory energy derived from the stabilized ring oscillator is first impressed upon an intermediate amplifier arranged to permit signalling by keying or modulating of the high frequency oscillations passing through the amplifier. The modulated output of'this intermediate amplifier is then impressed upon a power amplifier which delivers its oscillatory energy to the antenna. By such arrangement disturbing reactions resulting from the modulations of the power delivered to the high frequency radiator are prevented from influencing the operation of the ring circuit oscillator while the ring circuit, on the other hand, retains full stabilizing control of the oscillations. Furthermore, disturbance of the ring oscillator and its stability, due to keying or modulation of the output of the intermediate amplifier is prespectively,

vented by arranging the keying or modulatin means so astoprevent'feed-back or reaction on the ring oscillator. I

r In the embodiment, of the invention shown in the drawings the intermediate amplifier TA con sists of three impedance-coupled-amplifier stages including three audion tubes V3, V4 and V5; These audion tubes are'of the screen grid type and comprise, respectively, filamentary cathodes 36, 3'7, 38, control grids 39, 40, 41, anodes or plates 42', 43, 44'and screen grids 45, 46, with associated elements including cathode-heating source 48, plate current-source 49, grid-biasing source 50, high frequency choke coils 51, 52, 53, and by-pass condensers 54, 55, 56. 'Input impedances in the form of inductances 57, 58, 59 are connected, re-

in the input circuits of the three tubes V3, V4, V5, and in the output circuits are connected tank circuits LC3, inductances 60 and '61. Thecontrol grid 39 of the first tube of theintermediate amplifier stage is connected toa tap on the inductance ll'of the tank circuit LC2 of the ring oscillator TO, and'the input electrodes of the further amplifier tubes V4, V5 are similarly connected to the inductances 60 in the tank circuits of the preceding amplifier tubes, blocking condensers62, 63, 64 being provided in theseveralconnections, respectively.-

In the output circuit of amplifier tube V5 of the last stage-of the intermediate amplifier TA there is provided-a transmitter key TK by means of which the uni-directional current supply'source 49 may be out off from the plate circuit of the last tube. In this way the oscillation in the last stage of the intermediate amplifier may at any timebe cutoff or established vby opening or' closing. the key TK. 1

The so modulated output from the intermediate amplifier TA is impressed upon a final power amplifier stage TPA comprising a screen grid amplifier tube V6, having a cathode '70, a control grid 71, anode '72 and screen grid 73 withv the associated cathode-heating source '74, a plate current source '76, high frequency choke coil '77' and bypass condensers '78, '79, 80. A tank'circuit LC6 comprising an inductance 81 and a condenser 82 is connected in the input circuit of the tube, and a tank circuit LC7 comprising an inductance 83 and a condenser 84 is connected in the output of the tube. The output of the last tube V3 of the'int'ermediate amplifier is im pressed upon the input circuit of the power amplifier TPA through a coupling connection 85 including a blocking condenser 86. The output circuit of the power amplifier tube V6 is OOH. nected with the radiating antenna RA by means of a coupling transformer 8'7, which is preferably connected to the midpoint-of the antennathrough condensers 88 and is arranged to permit balancing of the currents in the two antenna halves and to adjust the degree of coupling with the output circuit of the amplifier tube.

The several amplifier stages TA and TPA are .so arranged that they shall not by themselves come .into an oscillatory state, andwith this in view the several screen grid electrodes are connected and adjusted to prevent feed-back from the output circuits to-the input circuits. The tank circuits LC3 to LC'7 are preferably resonant to the frequency of the particular subchannel so as to exercise a further discriminatingefiect, although there may be used untuned or aperiodic circuits that merely cooperate to amplify the oscillatory input received from the reentrant ring oscillator.

L04, L05, composed or In operating 'a transmitter of the type described above the reentrant ring oscillator TO is caused to oscillate with low energy, the tank circuits LCl and LC2 being tuned to the frequency on which the subchannel is to operate. Energy from this stabilized ring oscillator is impressed upon the intermediate amplifier TA with its stages V3, V4, V5 where the weak energy received isamplified-to a substantial value and is keyed so as to produce the desired signals. The point where the keying is effected is so chosen as to prevent disturbing reactions that might be caused'by the keying from afiecting the operation of the ring oscillator TO, and it isfor this reason that one or more amplifier tubes V3, V4 are connected between-the stage where the keying is done and the ring circuit. The keyed high frequency oscillations from the last stage of the intermediate amplifier are then conveyed to the power amplifier TPA where the oscillatory energy is further amplified to a value at which the desired radiation will be produced. As indicated in the drawing the subchannels C2, C3, C4, C5 have transmitting oscillators TO and intermediate transmitting amplifiers TA which are duplicates of the apparatus used in the subchannel C1. One power amplifier TPA may be used for several subchannels, and in the drawings the outputs of the intermediate amplifiers TA of all the five subchannels are shown connected .to the common coupling conductor of the power amplifier TPA so as to impress the outputof allthe five subchannels on the same power amplifier. Where the input or output circults-of the power amplifier TPA are tuned, the tuning is made sufficiently broad to prevent discriminatory action against the high frequency currents received from the several subchannels operating on. the same power amplifier." The individual high frequency channels are keyed separately and their combined input is impressed upon the amplifier. 'As'a result the output of the power amplifier thatis impressed upon the radiating antenna will represent a resultant of the oscillations impressed by the individual sub channels which. operate on it.

Although in certain applications it may be desirable to operate a plurality of intermediate amplifiers of difierent subchannels with a single power amplifier of broad tuning to cover the rangeof the several subchannels operating on it,

I prefer in ordinary point to point transmission,

to use a separate power amplifier for each of the subchannels. With such arrangement each subchannel has its own transmitting oscillator TO, its own intermediate amplifier TA with keying arrangement, and its own transmitting power amplifier TPA.' The radiating antenna may be used in common for all the subchannels, or a separate radiating antenna may be used for each subchannel. Where the radiating antenna is used in common, it is made so as to avoid any discriminatory effect on the individual frequencies that are'to be radiated by it. i

In order to supervise the operation of the transmitting apparatus, it has associated therewith the monitoring systemv shown in Fig. 1 of the drawings. The monitoringsystem of the subchannel CL is shown in detail, and comprises a monitor beat oscillator MBO, a monitor beat receiver MBR, a monitor beat selector MBS, a

standard monitor oscillator SMO and a monitoring stage MU.

audion tube V'7.having a cathode 90, a control rid 91, and an anode 92 with the associated cathode heating source 93, plate source 94 and by- -pass condenser 95. A tuned tank circuit L08 comprising an inductance 96 and a condenser 97 is connected in the output circuit of the audion tube V7 and a piezo-electric crystal oscillator 98 is connected in the input circuit of the audion tube in such manner as to produce in the tank circuit LC8 a continuous oscillation at the frequency of the crystal oscillator 98. This monitor beat oscillator is so arranged and adjusted that the frequency of its oscillations differs slightly from the frequency of the oscillations produced by the transmitter apparatus so that when the frequency of the monitor beat oscillator is combined with the frequency of the transmitter osv cillator a beat frequency will result which is preferably within the audible range. For ,instance, assuming that the frequency of the transmitting subchannel C1 is 5,875.00 kilocycles, the beat oscillator MBO is adjusted to oscillate at a frequency of 5,872.375 kilocycles, giving a beat frequency of 2625 cycles. 7

This beat frequency is produced in the monitor beat receiver MBR which comprises an audion tube V8 having a filamentary cathode 100, a control grid 101, an anode 102 withthe associated cathode-heating source 103, plate supply source 104 and by-pass condensers 105, 106. Oscillations from the reentrant ring oscillator T0 of the transmitter are impressed upon the input electrodes of the monitor beat receiver MBR by means of the coupling coil 107 arranged to be variably coupled to the coil-20 in the input circuit of the tube V1 of the ring oscillator. Oscillations from the monitor beat oscillator are simultaneously impressed upon the monitor beat receiver MBR by means of a coupling circuit 108 including a coil 109 coupled to the inductance 96 in the tank circuit L08 of the monitor beat oscillator MBO and a coil 110 coupledto a coil 111 that is connected in the input circuit of the monitor beat receiver, being arranged in series with the coupling coil 107 of the ring oscillator TO. A condenser 112 connected in shunt to the circuit including the coupling coils 107 and 111 serves to adjust the input circuit to secure optimum operation conditions. The circuits of tube V8 are adjusted, as by suitable bias on grid 101, to deliver rectified beat oscillations on the output side to an audio frequency transformer 113 through which the oscillations are impressed on the monitor beat selector MBS.

The monitor beat selector MBS comprises two cascade coupled screen-grid audion amplifiers V9 and V10 having cathodes 115, control grids 116, anodes 117 and screen grids 118, with the associated cathode heating source 119, plate current source 120, choke coils 121 and by-pass condensers 122, 123. In the plate circuits of the two tubes are connected tank circuits L09 and LC10 formed of inductance coils 125 and condensers 126, the tank circuits L09 and LC10 being tuned to resonance with the beat frequency of the particular channel. The input electrodes of audion tube V9 are coupled to the output circuit of the monitor beat receiver by a variable tap connection 127 on a coupling resistor 128 connected to the output transformer 113. The input electrodes of the audion tube V10 are similarly connected through a variable tap resistor 129 to the output circuit of the audion tube V9, a blocking condenser 130 being interposed in the connection. A standard monitor oscillator SMO associated with the subchannel is arranged to produce an oscillation of the same frequency as the beat note derived from the monitor beat selector MBS, in this particular instance, an oscillation of 2625 cycles. The standard monitor oscillator comprises two tubes V12, V13, having cathodes 140, anodes 142, control grids 143 with associated cathode heating source 145 and plate current source 146. In the input circuits of the two tubes V12, V13 are connected tank circuits LC12, LC13 composed of inductances 147 and condensers 148 tuned to the frequency of the oscillation, in the present instance, to frequency of 2625 cycles. The two audion tubes. V12, V13 are coupled in a ring circuit in a way similar to the transmitter oscillator TO, the plate 142 of one audion tube being connected to the grid, 143 of the other audion tube through connectors including current limiting resistors 151 and blocking condensers 1.52. Audio frequency choke coils 153 and bypass condensers .154 complete the circuits.

This arrangement of the'two valves V12, V13 in a ring circuit will result in generation of, oscillations of a frequency of the tank circuits LC12, LC13 in a manner similar to the'operation of the transmitter oscillator TO, the oscillations being very stable at the particular frequency of the tank circuits and being practically unaffected by disturbances that tend to vary'or shift the frequency of the oscillations.

The outputs of the monitor beat selector MBS and the standard monitor oscillator SMO are impressed on two tubes V11, V14 of the monitoring unit MU in such manner as to permit comparing of the frequencies of these two outputs and ascertain as to whether the beat oscillation differs from the standard monitor-oscillation orv not. Audion tubes V11 and V14 each comprise a cathode 161, an anode 162, control grid 164 with associated cathode-heating source 165 and plate current source 166. The input electrodes'of tube V11 are coupled to the output circuit of the monitor beat selector by a connection including a variable tap impedance 167 and blocking condenser 168. The input electrodes of the audion tube V14 are similarly connected to the output circuit of the tube V13 of the standard monitor oscillator SMO by a variable tap resistor 169. The output circuits of the two tubes V11 and V14 are impressed through coupling transformers 171 and 172 on a monitoring device 173 which is arranged to be actuated by the two frequencies received from monitor beat selector MBS and standard monitor oscillator SMO, respectively, to indicate any departure from the standard. As shown in the drawings, provision may also be made for connecting additional auxiliary apparatus such as head telephone sets to the output circuits of'the two audion tubes V11 and V14, as by means of telephone jacks 174 and 175, permitting direct comparison of the two audio frequencies'by telephone.

In the foregoing arrangement, the monitoring system maintains a continuous supervision of the operation of the'transmitting apparatus of each subchannel. Simultaneously with the generation of high frequency oscillations in the transmitter oscillator TO a part of its ouput is impressed upon the monitor beat receiver MBR where this output is combined with the output of the monitor beat oscillator MBO. -The resulting beat note is then picked out by the monitor beat selector MIBS and delivered in amplified form to the monitoring unit MU that independently receives oscillations from a standard oscillator SMO which is so set that by comparison of its frequency with that of the beat note in the monitoring unit MU, it is immediately may be substantially identicalwith the apparatus possible to determine whether the transmitter oscillator T0 is in time and'operates within its assigned frequency band or has deviated therefrom, necessitating corrective adjustments.

.In the drawings I have shown the monitor beat oscillator MBO in the form of a piezo crystaloscillator and the standard monitor oscillator SMO in the form of a specialreentrant 'ring'oscillator. For .the satisfactory operation of the monitoring system both the monitoring beat oscillator and the standard monitor oscillator must maintain their frequency very closely and operate stably Without deviations from their predetermined frequencies. Instead of a piezo electric oscillator,

-a reentrant ring oscillator may be used as a monitoring beat oscillator, and conversely, a .piezo electric oscillator may be employed as a 'standard monitoring oscillator SMO.

Where the apparatus for each subchannel is made complete in itself, each subchannel will have its own monitoring beat oscillatorLMBO,

monitor beat receiver MBR, monitor beat selector MBS, standard monitoring oscillator SMO and monitoring unit MU. However,'where several subchannels .are combined as in the arrangement illustrated in the drawings, a single monitor beat oscillator may be used for several subchannels. Assuming the instance referred to above, where the 'five subchannels are arranged for operation at 5,873.50 kilocycles, 5,874.25 kilocycles, 5,875.00 kilocycles, 5,875.75 vkilocycles and 5,876.50 kilocycles, the monitor beat oscillator is arranged so as to oscillate at a frequencywhich will permit combination of its oscillations with the. frequencies of the several subchannels so that for each subchannel there is produced a monitoring beat oscillation of an audible frequency. Thus in the-specific case mentioned, the monitoring beat oscillatormaybe set for operation at a frequency of 5,872.375 cycles, giving for the .five subchannels beat'oscillations of 1125 cycles, 1875 cycles, 2625 cycles, 3375 cycles and 4125 cycles. In order to secure satisfactory operation and permit a proper selective action of the monitor beat selectors of the several subchannels, the beat frequencies of subchannels operating with a common -m0nit01' beat oscillator should be in such relation that the beat frequency of one subchannel isg not a harmonic of the beatfrequency of the other subchannel. This is secured byproper choice of the frequency 'of the monitor abeat oscillator with respect to thefrequencies of the several subchannels with which it is tocoo'perate in: the The remaining apparatus described in detail in connection with the sub channel C1, each channel being setfor its particular beat frequency.

The receiving apparatus shown in' Figs. 3 and 4 of the drawings comprises a reception input amplifier RIA, a reception beat detector RBD,a reception beat amplifier RBA, a receptionchannel selector RCS, a reception channel .amplifier RCA, a reception channel rectifier RCR and" a reception relay RE.

The reception input amplifier comprises a screen grid audion tube W1 having a cathode 201, an anode 202, a control grid 203, and a screen grid 204. The input from an aerial AB is impressed upon the input electrodes of tube W1 .across an input impedance 205, and an output impedance 206 is connected to the output electrodes .of the tube' W1, blocking condensers 207 and 2'03 completing the'circuits.

: The radio beat 'detectorRBD comprises audion tubes W2, W3, having cathodes 210, anodes 211 and control grids 212, the tube W having also a screen grid 213. JA tank circuit CLl comprising an inductance 215 and a condenser 216 is con- .nected across the input terminals of the tube W2. A tank circuit GL2 comprising an inductance 217, and a condenser 218 is connected in the output circuit of tube W2, by-pass condensers 219 and 220 completing the circuit connections. A non-selective impedance 221 isrconnected across the input electrodes of audion tube W3, and a primary winding of an audio frequency coupling transformer'222 is connected to the output electrodes of audion tube W3, by-pass condensers 224 and 225 and high frequency choke coils. 226 completing the circuit connections. The two audion tubes W2 and W3 are connected in a reentrant ring .circuit similar to the reentrant ring circuitof' the transmitter oscillator TO by, means of coupling connections 227, 228, including blocking condensers 229, .230. A cathode-heating source '231 and a plate and screen grid biassource 232 completes the circuit connections of the three tubes W1, W2 and The tank circuits CL1 and CL2 are so adjusted 0 that their frequency difiers from the frequency of the received oscillations so that on combination therewith, a beat note. of audio frequency will be produced... Forinstance, assuming that the received frequency is.5,8.75.00 kilocycles, the tank circuits CLl and CL2 are tuned for a frequency of 5,872.375kilocycles so that when the two frequencies are combined a beat frequency of 2625 cycles will result. 'The circuits of tube W3 are adjusted-to deliver rectified beat currents to the output transformer 222, feeding the high frequency currents back to the input of tube W2.

I have found that such ring circuit in which the externally received oscillatory input is con-' .Qring filter circuit amplification, there is obtained a stable beat oscillation; and the aperiodic character of g-theinput and output circuit of the secondtaudion tube W3 of the ring circuit permits effective amplification of the audio beat frequency so thateven very weak incoming signals will give a clear and ample beat note that is suitable for further amplification and reproduction of the signal.

.The reception beat amplifier RBA comprises audionv tubes W4, W5 havingv cathodes 235, anodes 236, and grids 237, with ass'ociatedgridbiasing source 238 and plate source 239, the oathodes being supplied from the cathode supply source 231 referred to before. The output of the audio frequency couplingtransformer 222 of the radio beat detector RB'D is impressed upon the input electrodes of amplifier tube W4, and the output of" this tube is'impressed through the audio frequency coupling transformer'240 upon the input electrodes of the second amplifiertube -W5. The output of thelatter tube is impressed upon-a .coupling'transformer 241 which delivers throughc'onductor 242, amplified beat frequency currents to the radio reception channel selector RGS.

The reception channel selector RGS comprises screen grid tubes W6 and W7 having cathodes 251, anodes 252, control grids 253, and screen grids 254, withassociated cathode heating source 255, plate current source 256, audio frequency choke coils 257 and by-pass condensers 258, 259. Tank circuits GL6, GL7 composed of inductances and condensers are connected to the output electrodes by the audion tubes W6 and W7, and adjustable-tap input impedances 261, 262 are connected in the input circuits of the two tubes respectively. The amplified audio beat frequency currents derived from the output transformer 241 are impressed through conductor 242 upon the input impedance 261 of audion tube W6 which serves to amplify the received beat frequency and to select through its tank circuit GL6 the frequency to which tank circuit GL6 is tuned, suppressing other frequencies. The amplified output from tube W6 is impressed through conductor 264 including blocking condenser 265 upon the input impedance 262 of audion tube W7 which further amplifies and through its tank circuits GL6, GL7 exercises a further selective action on the impressed beat frequeneiea. As a result, the reception channel selector selects from the beat frequencies derived from the. reception beat detector a beat frequency current having a frequency corresponding to the frequency of the particular subchannels. The selected beat frequency is at the same time amplified so that it is in sufiicient strength for utilization in the further apparatus.

The output of the reception channel selector is impressed through an input impedance 27-1 upon a reception channel amplifier RCA which comprises an audion tube W8 having a cathode 272, an anode 273 and control grid 274, with the associated cathode-heating source 275, plate current source 276, audio frequency choke coil 277 and by-pass condenser 278. The amplified output of theaudion tube W8 is then passed through a reception channel rectifier unit RGR comprising a double wave rectifier tube W9 and an amplifier tube W10. The rectifier tube W9 comprises double wave cathodes 281 and two anodes 282 cooperating therewith. An audio frequency tra'fisformer 284 has aprimary winding 285 connected to the output terminals of the amplifier tube W8,-and a mid-tap secondary winding 286 connected to the anodes 282 of the rectifier tube W9. The rectified output is then derived through conductors connected to the cathodes 281 and to the mid-tap of the secondary transformer winding 286, and impressed upon the input impedance 287 of the amplifier tube W10 having a cathode 288, anode 289 and control grid 290.

A cathode-heating source 291 supplies, the

cathodes of the tubes W9, W10 and a plate curception channel amplifier, as by means of a jack 297, or by means-of a secondary of a transformer 298 connected across the output terminals of audion tubeWS.

In operationv of the receiving system described above, the modulated impulses reaching the aerial AR of the receiver produce a circulation of cur- I:

rent in the receiver antenna. These currents are amplified in the amplifier tube W1 which, as pointed out above, is not critically selective. The amplified oscillations are then impressed on the reception beat detector RBD where a local oscillation is combined with the received signals to produce a beat note which is then amplified in the several amplifying stages of the reception beat amplifier RBA. The amplified beat frequency currents are then impressed upon the several stages of the reception channel selector RGS where the beat frequency currents having the frequency of a particular subchannel are selected and amplified and then impressed upon the re ception channel amplifier RGA for further amplification. The output of the latter amplifier is then rectified through the rectifier tube W9 and after further amplification in the tube W10 the signalling currents so derived are impressed upon the relay RE for actuating the telegraph recording or similar apparatus at the receiving station.

The arrangement described above is particularly useful when employed for the reception of signals of a number of subchannels. vAs shown in the drawings, the receiving system may be arranged for reception of signals transmitted, for instance, on five adjacent subchannels corresponding in this particular example to the five subchannels of the transmitting stations, i. e., for the subchannel frequencies of 5,873.50- 5,874.2505,875.00--5,875.755,876.50 kilocycles respectively. For such multiple channel receiving system I do not employ a complete set of receiving apparatus as described above for each subchannel, but I employ the reception input amplifier, reception beat detector and reception beat amplifier in common for the several subchannels. With such arrangement, the circuits and the elements of the reception input amplifier RIA, re-

ception beat detector RED and reception beat amplifier RBA are so designed and correlated as. to be substantially equally sensitive to high frequency signals of all the five subchannels that are to be picked ceiving apparatus.

Assuming, for, instance, thatthe transmitting apparatus described in conjunction with Figs. 1 and 2 radiates a high frequency output which is a combination. of signal-modulated energy of up by the particular rethe five subchannels, G1, C2, C3, C4, C5 of the subchannels of the transmitting station an audio beat frequency in the same way as the monitor beat oscillator. Thus, in the present instance, the local oscillations of the reception beat detector combined with the incoming signals of the five'subchannels of the transmitting apparatus willgive an output which is the resultant of five modulated beat frequencies of 1125 cycles, 1875 cycles, 2625 cycles, 3375 cycles and 4125 cycles. The resultant currents of these five beat frequencies aretthen further amplified'in the reception beat amplifier and then impressed through the common conductor 242 upon the reception channel selectors RCS of the five subchannels C1, C2, C3, C4, C5. A separate reception channel selector ROS, reception channel amplifier RCA, reception channel rectifier RCR. and reception channel relay RE is provided for each of the five subchannels.

The tanks of the reception channel selectors RCS of the five subchannels are tuned to the five different beat frequencies corresponding to the frequencies assigned to the five subchannels, that is, to the frequencies of 1125 cycles, 1875 cycles,

2625 cycles, 3375 cycles and 4125 cycles, so that each reception channel selector picks out from the combined output of the reception beat amplifier RBA impressed upon the common conductor 242 only the currents of the beat frequency corresponding to the particular channel, and these selected beat-frequency currents are then impressed upon the further apparatus of the particular channel for actuating the recording or other telegraph signalling apparatus.

I have found in practical tests that by utilizing radio transmitting and radio receiving systems as described above, very good communication without interference may be obtained along closely spaced subchannels and that by the use of this arrangement, it is possible to obtain within the available radio spectrum a much larger number of communication channels than by the other systems proposed heretofore.

A particular advantage of the system described above is the fact that a plurality of subchannels operating on closely adjacent frequency bands are operated in combination as if they were parts of a single channelin such manner that there is excludedthe possibility of interference with other communication channels. This is made possible by the combination of the signalling energy of a plurality of subchannels in the transmitting station and the radiation of a combined wave representing the resultant of the signalling energy of the five subchannels at the transmitting station; and the cooperation therewith of a receiving arrangement in which the received resultant radiations of the transmitting stations are amplified, stepped down by beat frequency oscillator amplifier and then the resultant beat frequency resolved in its component beat frequencies corresponding to the beat frequencies of the several subchannels.

While a complete transmitting and receiving system is shown in this application including the special oscillator constituting a part of the invention, only the transmitter is claimed herein as the other features disclosed will be separately claimed in other applications and are shown here merely by way of illustration as being closely related to the transmitter per se.

The invention resides not only in the general arrangement of apparatus and systems as described above but also in the specific arrangements of the apparatus of the various elements of the system which are applicable to a variety of other uses than those described herein. Many modifications of the arrangements and details will suggest themselves to those skilled in the art, and it is accordingly desired that the appended claims be given a broad construction commensurate with the scope of the invention within the art.

I claim: i

1. In a radio communication system, a plurality of apparatus sets for producing oscillations of aplurality of different but closely adjacent frequencies to operate a plurality of distinct communication channels, each set having a low energy master oscillator arranged to continuously produce oscillations of a frequency assignedto the particular communication channel, an, amplifier for amplifying the output of said master oscillator, a second amplifier and meansassociated therewith for modulating the oscillatory output thereof underelimination of reactions on said master oscillator through the interpositioning of said first amplifier between said master oscillator and said modulating means, a power. amplifier connected to the output terminals of all of the amplifiers of the several sets for combining the modulated output of the amplifiers of said sets and for further amplifying the combined output, an aerial for radiating the combined amplifier output of said power amplifier, said power amplifier being substantially equally effective in amplifying the output of the apparatus of the several communication channels connected to it while discriminating against oscillations of frequencies remote from the frequencies of the individual channels connected to it, means for heterodyning the unmodulated output from each of said master oscillators with a standard source of high frequency energy differing from the frequency of each of said master oscillators an amount such that relatively low frequency beats will be produced between saidstandard source and each of said master oscillators, and means for comparing each of said low frequency beats with a standard generator having a frequency equal to the normal frequency of the beat to whichitis to be compared. 3

2. In a radio communication system, a power amplifier including audion tubes having input and output electrodes, a radiating aerial connected to said output electrodes, a plurality of channel oscillators arranged to oscillate at different frequencies for independently operating a plurality of distinct communication channels, an amplifier for each channel oscillator arranged to amplify the output thereof, a second amplifier arranged to further amplify the output from each of said channel oscillators, means associated with said second amplifier for modulating the amplified oscillations under elimination of reactions on said channel oscillator by means of said first mentioned amplifier which is caused to act as a buffer between said channel oscillator and said second modulated amplifier, means for connecting the output electrodes of each of said channel amplifiers to the input electrodes of said power amplifier for combining therein the individually modulated oscillatory energy derived from said plurality of channel oscillators, means for heterodyning the unmodulated output from each of said master oscillators with a standard source of high frequency energy differing from the frequency of each of said master oscillators an amount such that relatively low frequency beats will be produced between said standard source and each of said master oscillators, and means for comparing each of said low frequency beats with a standard generator having a frequency equal to the normal frequency of the beat to which it is to be compared.

3. In a radio communication system, the combination with transmitting apparatus for a plurality of communication channels comprising a master oscillator for each channel, means for amplifying and modulating the oscillations of for radiating the modulated energy of each channel, of monitoring means for said communication channels comprising a standard oscillator arranged to oscillate at a frequency differing from the frequencies of all of said master oscillators, means for combining oscillatory currents derived from all of said master oscillators with the output of said standard oscillator to produce a combined beat current which is the resultant of beat currents of all of said master oscillators, means for selecting from the combined beat output beat frequencies corresponding to the combination of the oscillation of said standard oscillator with the oscillations derived from each master oscillator, and means for individually monitoring the several beats with'standard oscillations of corresponding frequencies.

4. In a radio communication system, a plurality of apparatus for generating continuous high frequency oscillations of different frequency to operate a plurality of distinct communication channels, means for independently keying each separate channel, a low frequency standard oscillator for each channel and a common high frequency monitoring oscillator for the system, said common high frequency oscillator being adjusted to produce heterodyne beats of relatively low frequency with each of said plurality of high frequency generators, and means for continuously comparing said low frequency beats each with said low frequency standard oscillator, each of said low frequency oscillators being adjusted to produce a frequency of the same value as that of the beat normally produced between the com,- mon high frequency oscillator and the one'of aid plurality of high. f qu n y n r to s t whi h sa d ow f qu n y st ndard is bein omparedthe master oscillator of each channel, and means 5. In a radio communication system, a plurality of channel oscillators for generating continuous high frequency oscillations for the purpose of effecting multi-channel communication, a single standard oscillator of slightly different frequency from thechannel oscillators, means for heterodyning between the standard oscillator and the separate channel oscillators,thereby producing aplurality' of beats substantially within the audio range of frequency, means for selecting, detecting and amplifying these beats and means for comparing these beats with a standard audio oscillator having a frequency, the same as that of the beat normally obtained between the channel oscillator and the high frequency standard oscillator.

6. In a multi-channel radio communication system, the combination with a transmitting apparatus for each channel comprising a master oscillator, an amplifier for amplifying energy derived from said oscillator, means for modulating the amplified energy, a power amplifier for amplifying simultaneously oscillations from all saidchannels, and an aerial for radiating the modulated amplified energy from said last amplifier, of a monitoring system comprising a standard oscillator arranged to generate an oscillation differing from the frequency of one of said master oscillators by an audible frequency, means for deriving an unmodulated oscillatory current from any of said masteroscillators and combining it with the output of said standard oscillator to produce an audible beat note, a second standard oscillator arranged to produce an oscillation of the frequency of said beat note, and means for monitoring the oscillation of said second standard oscillator against the derived beat oscillation of one of the master oscillators.

' EARL L. KOCH. 

